Spindle assemblies for grinding wheels

ABSTRACT

A GRINDING WHEEL SPINDLE ASSEMBLY COMPRISES AN HYDRAULIC MOTOR ARRANGED TO DRIVE A ROTATABLE PART FOR CARRYING A GRINDING WHEEL, CONTROL MEANS WHEREBY THE FLOW OF FLUID IS VARIED AS DRESSING OF THE WHEEL TAKES PLACE, AND THEREFORE CHANGES IN ITS DIAMETER, SUCH FLOW CHANGES VARYING THE SPEED OF ROTATION OF SAID PART TO MAINTAIN THE PERIPHERAL SPEED SUBSTANTIALLY CONSTANT.

P. A. MASON Jan. 5, 1971 SPINDLE ASSEMBLIES "FOR GRIND ING WHEELS Filed Nov. 14, 1967 lm w ll ifsPw l lllhh. 27 I |m |1 IMMRWRQ .o

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ATTORNEYS United States Patent C 3 552 064 SPINDLE AssEMBLIEs For: GRINDING WHEELS Peter Alan Mason, Kenilworth, England, assignor to Wickman Machine Tool Sales Limited, Coventry, England Filed Nov. 14, 1967, Ser. No. 682,778 Claims priority, application Great Britain, Nov. 18, 1966, 51,780/ 66 Int. Cl. B2411 7/00, /00, 53/00 US. Cl. 51-5 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to grinding wheel spindle assemblies, particularly, though not exclusively for use upon profile grinding machines to support a grinding wheel which is rotated and also reciprocated, so as to perform I a series of successive grinding operations upon a workpiece.

In most known profile grinding machines, the spindle is rotated through a belt drive from a motor which is relatively remote from the spindle itself, there being means for maintaining belt tension as the body upon which the spindle is mounted reciprocates. Such an arrangement employing belts imposes limitations on the torque that can be transmitted, and in addition suffers from the disadvantage that the reciprocating travel of the grinding wheel is limited in accordance with the dictates of the belt tensioning mechanism, and the speed of rotation of the grinding wheel varies between the ends of its permitted travel, giving rise to belt slipping.

Furthermore, as the grinding wheel diameter reduces as a result of Wear and dressing, the average peripheral speed of the wheel changes.

The object of the invention is to therefore provide a grinding wheel spindle assembly in a form in which these disadvantages can be overcome or substantially reduced.

In accordance with the present invention there is provided a grinding wheel spindle assembly including an hydraulic motor, means for admitting fluid under pressure to the motor to drive a rotatable part of the assembly to which the grinding wheel is to be attached, and control means for varying the flow of fluid through the motor at intervals coinciding with dressing of the wheel, and therefore with changes in its diameter, such flow changes varying the speed of rotation of the grinding wheel to maintain the peripheral speed thereof substantially constant.

Preferably the hydraulic motor has radially recriprocable balls mounted in cylinders formed in the rotatable part of the spindle assembly.

Preferably also the rotatable part is mounted for rotation within a housing by means of hydro-static bearings, means being provided for suppying hydraulic fluid thereto from the same source which provides fluid for the hydraulic motor, but at a different pressure.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view in side elevation of a grinding wheel spindle assembly constructed in accordance with the invention, and

FIG. 2 is an enlarged cross-sectional view of a stationary inner part of the assembly,

FIG. 3 is'a cross-sectional view on the line III-III of FIG. 2, and

FIG. 4 shows, diagrammatically, an hydraulic circuit with the spindle.

The grinding wheel spindle assembly shown is intended for use in a profile grinding machine.

The spindle assembly is mounted in a body indicated at 10 whichis mounted for vertical reciprocation upon a suitable structure (not shown) on the grinding machine, and comprises a stationary housing 11 within which is a rotatable part 12.

One end of the part 12 extends out of the housing 11 through a detachable end cap 13, and this portion of the part 12 is intended to carry the grinding wheel a, and for this purpose is tapered, as illustrated. The part 12 is mounted within the housing 11 in a pair of hydrostatic bearing assemblies indicated at 14 and 15 respectively. Each such hydrostatic bearing assembly is of conical form, and they are arranged with their smaller ends presented away from one another. Fluid under pressure is supplied to the bearing assemblies 14, 15 through passages 16, 17 respectively in the housing 11, these being supplied from a pump b obtaining a supply of fluid from a reservoir 0. The pump outlet is connected through pipes d and e to an inlet 18 in the housing. The passages 16, 17 are formed by tubes secured in grooves in the external surface of the housing 11, connecting with the bearings through annular recesses 14a, 15a and thence through passages 14b, 15b to appropriate pockets within bearings 14, 15. Defined between the housing 11 and the body 10 within which the assembly is mounted, is a drain gallery 19 with which communicates an outlet connection 20 for the recovery of fluid which has been supplied to the bearings. A pipe f leads from the outlet 20 to the reservoir 0.

The opposite end of the part 12 from the grinding wheel attachment end is provided with a concentric bore 21 extending over approximately half the length of the part 12. In the wall of the part 12 and communicating with the bore 21 are two axially spaced sets of radially extending stepped bores 22. The larger outward portion of each such bore 22 is provided with a sleeve 23 of a hard ma terial such as tungsten carbide, and within each of these is mounted a piston, which in this example is a ball 24 which is capable of moving radially with respect to the axis of the spindle proper.

Surrounding the part 12 adjacent to the sets of radial bores 22, are a pair of eccentrically mounted rings 25, 26 respectively, each provided with an internal annular groove within which the balls 24 are engaged. Surrounding the rings 25, 26 are respective packing rings 27, 28 each of which is engaged by screws (not shown), these screws maintaining the eccentric position of the rings 25, 26, 27, 28 with respect to the bearing assembly 15, at the adjacent end of the part 12.

Within the bore 21 of the part 12 is a stationary member 30. In the member 30 are formed two axially spaced pairs of crescent shaped recesses 31, the recesses of each pair being diametrically opposite, as illustrated in FIG. 2 of the drawings. The pairs of recesses 31 are moreover axially aligned with the bores 22 in the part 12 respectively. Also in the member 30 are two spaced axially extending bores 32, 33, one of which, 32, is in communication with the inlet 18, though, under different pressure to that supplied to the bearing assemblies 14, 15 and the other passage 33 is the return drain and communicates with the outlet 20. For leakage fluid there are, in the end of the bore 21, further radial passages 34 communicating with an annular gallery 35 in the housing 11 from which is a passage 36 communicating with the space 19 for the return of fluid outlet connection 20.

The passage 32 communicates through two passages 32a with one of each pair of crescent shaped recesses 31, 

